When turning, you want the cutting edge to be right on the centerline. What
I do is (with the machine off) pinch a small scale (ruler) in between the
bit and the work piece until it just stays without falling. If the top of
the scale tips toward you your cutter is low. If it tips away your bit is
too high.


you would want it very slightly high, so that under load it is near
centerline, but never low, or so I was taught